Why do penguins waddle?

Penguins waddle because it is the most efficient way for them to move around on dry land. With short legs and big feet, waddling allows penguins to propel themselves forward using the momentum of the side-to-side movement in order to use less energy to move around.

Short legs, big feet and chubby bodies make the penguins efficient swimmers who can survive in the freezing temperatures in which they live, but this body type makes walking a little more difficult. Waddling helps raise their center of mass when they walk, reducing the strain on their muscles as they move along on the icy terrain.